This invention relates to a process for manufacturing a band-shaped non-woven product with increased tensile strength, longitudinally and/or in the cross direction of the band-shaped product, as well as to the band-shaped non-woven products manufactured according to this process.
It is the aim of the invention to realize a band-shaped non-woven product of the above discussed type, the tensile strength (according to DIN 53857) of which is increased longitudinally, in the cross direction, or in both directions.
Non-woven products of the kind referred to, and having such characteristics, find a remarkable application as a geotextile or as a carrier for bituminous roofing bands.
In European patent application EP-A-0.506.051 it is proposed to reinforce a non-woven structure having a specific weight with polyester filaments showing an elasticity comparable with that of the non-woven structure. The strengthening filaments are applied between two layers of non-woven material and fixed by making use of a binder and thermo-mechanical means.
The strengthening of non-woven products has already been proposed in the following documents: GB 2 169 930 A and U.S. Pat. No. 5,219,633. In the former reference, essentially the elasticity of the product is considered, and not the application of the process on band-shaped products essentially intended as a carrier for bituminous roofing bands is suggested. The increase of the tensile strength of such band-shaped non-woven products presents very specific requirements, especially when the tensile strength is considered exclusively longitudinally and/or in the cross direction of the product.
U.S. Pat. No. 3,576,687—Parlin describes a process for manufacturing an elongated band-shaped non-woven product. In this known process the fleeces are made of thermoplastic fibers and are deposited on warp threads by means of cross-lappers, which operate in a filling direction. The fibers are deposited in a fluffed-up condition on the warp threads as the warp threads advance. When the desired thickness of the fibers has been deposited on the warp threads, the fibers, together with the warp threads, are subjected to the action of one or more needle looms in which barbed needles are forced through the deposited fibers.
A drawback of the process described in U.S. Pat. No. 3,576,687 is that the fibers in the fleeces are randomly oriented, which adversely affects the longitudinal strength of the product. Moreover, as the warp threads and the fleeces are both subjected to the needle looms, the longitudinal extension of the warp threads in the final product will be affected.
In the latter reference, the production of a non-woven material as a raw material for diapers, among others, is described, so it will be immediately clear that the process described in this reference complies with very specific requirements, and does not in any way provide any indication to the issue discussed here, i.e. the realisation of carriers for asphalt bands and geotextiles by strengthening of the tensile strength of the band-shaped product, specifically longitudinally and/or in the cross direction.